I have ib_udf.dll in /UDF directory on my Windows FB server install.

I have UDF F_LOWER as:
DECLARE EXTERNAL FUNCTION F_LOWER
RETURNS VARCHAR(255) FREE_IT
ENTRY_POINT 'IB_UDF_lower' MODULE_NAME 'ib_udf';

I have created a View:
CREATE VIEW V_View
( MY_VIEW) AS
select F_LOWER(MY_TABLE.FIELD1) from
MY_TABLE;

When I run this, I get an error:
ISC ERROR CODE:335544439
ISC ERROR MESSAGE:
function F_LOWER could not be matched

Please help.